Coal gasification is a leading and key technology for the clean and efficient utilization of coal. Entrained flow gasification is a new type of coal parallel flow gasification technology developed in recent decades. The gasification agent and coal powder or coal slurry enter a gasification furnace through a plurality of nozzles, the pyrolysis, combustion and gasification reaction of coal are carried out almost simultaneously. The high temperature in the gasification furnace ensures complete gasification of the coal, and the minerals in the coal become slag and leave the gasification furnace. Compared with the traditional gasification technology, the pressurized gasification process with an entrained flow gasification has the advantages such as high temperature, large processing capacity, high content of effective constituents in the fuel gas and high gasification efficiency. It presents the future development direction of the coal gasification technology, it is also one of the landmark coal chemical industry technologies which have been widely used in China and foreign countries, and are representatives of the advanced technologies in the world.
However, the coal chemical industry has been harshly criticized for its high water consumption and energy consumption, wherein the primary cause is the high water consumption and energy consumption of coal gasification technology. While in the coal gasification process, the chemical water consumption for the coal gasification reaction process is only ⅕ of the physical water consumption of the technological processes such as chilling and washing. Therefore, the pivotal issue of saving water in the gasification of the entrained flow gasification is to avoid and reduce the physical water consumption. However, the existing entrained flow gasification process, both the dry powder gasification and the coal water slurry gasification contain the step of discharging wet slag and the step of wetting and washing in the carbon wash tower, on the one hand, the steps consume a large amount of water, and result in a large amount of black water and salinity-containing wastewater which are difficult to treat, and the crystallization waste salts are hazardous chemical which can hardly be processed; on the other hand, the high temperature residual heat in the reaction process is not effectively utilized, thus the energy consumption is high; moreover, the difficulty in dehydration of wet slag and ash cake having a high content of carbon hampers the comprehensive utilization, and the dumping and landfill treatment is prone to cause secondary pollution. The aforementioned problems have become the biggest bottleneck to enhance quality and improve efficiency and obtain the clean, efficient and low carbon development for the coal chemical industry in the world.
At present, the co-generation technology of combusting coal powder and cogenerating cement clinker by controlling the ash composition is a hot research topic at home and abroad. However, due to the fact that the combustion temperature is at the critical reaction temperature of cement and the residence time is short during the gasification process, it causes that the solid-solid reaction strength and time period are insufficient or the ash content is difficult to control. Only a small number of processes have been subjected to pilot scale test or demonstration at present. In addition, the produced cement clinker has not achieved the desired effect, thus the poly-generation technology is still in a process of research and exploration.
In the existing gasification co-generation technology, the reducing atmosphere of the gasification furnace and the oxidizing atmosphere of the combustion furnace are different, which increase the difficulty to co-produce cement clinker from the coal powder gasification furnace and slag; in addition, the existing gasification furnace has a short residence time of the solid materials, and the ash and slag are in a blended status, which directly affect the properties of the co-produced cement; moreover, a process of discharging slag with a wet method may be extremely prone to cause the hydration reaction, thereby form the agglomeration and blockage.
Therefore, the research on the co-production of cement clinker from the coal powder and the gasification slag may solve the problem concerning how to perform large-scale resource utilization with high added value on the solid waste generated by the coal gasification process. Therefore, the pivot issue and key point for the future development of the entrained flow bed for performing the clean and efficient coal gasification co-generation technology reside in how to reduce the physical water consumption, sufficiently recover the thermal energy, and perform large-scale resource utilization with high added value on the gasification furnace slag.